1. Field of the Invention
The present invention relates to a method of manufacturing a multilayer electrolyte reinforced composite membrane and, more particularly, to a method of manufacturing an electrolyte reinforced composite membrane having an excellent mechanical stability and a superior hydrogen ion conductivity with a thin film membrane. Moreover, the present invention carries out a stretching process and a drying process an optimum number of times and provides a hydrogen ion exchange membrane of a three-layer structure that comprises: a matrix layer of a hydrogen ion exchange membrane impregnated and stretched with a polymer electrolyte; and electrolyte coated layers established on the upper and lower portions of the matrix layer. Accordingly, the present invention can lower the manufacturing cost and maintain the ion conductivity even under the conditions of low humidity and high temperature.
2. Description of Related Art
Polymer Electrolyte Membranes (PEMS) have been used as ion exchange membranes in polymer electrolyte membrane fuel cells (hereinafter, referred to as PEMFCs), chemical sensors, biofuel cells, etc. due to their functional properties. Recently, the development of fuel cells using hydrogen as a safe and clean fuel has attracted attention as the seriousness of resource depletion and environmental concerns is raised worldwide. Accordingly, with the growing application of PEMFCs to vehicles, mobiles, and other contexts, effort is being made on developing more stable polymer electrolyte membranes with good hydrogen ion conductivity.
As recognized by those of skill in the art, polymer electrolyte membranes in PEMFCs should serve a variety of functions, such as providing insulation between the anode and cathode and enabling hydrogen ion exchange. Moreover, polymer electrolyte membranes should ideally be chemically and physically stable and able to withstand conditions of high temperatures and humidity, low pH (less than pH 2) and high pressure. Accordingly, it is necessary to develop a better reinforced polymer electrolyte membrane and thereby enhance the performance and stability of PEMFC.
Conventional ion exchange membranes in use include perfluorinated polymer electrolyte membranes (perfluorinated sulfonic acid PFSA or perfluorinated carboxylic acid PFCA), which have excellent chemical stability and good ion conductivity (˜1.0 S/cm) under humid conditions. These conventional membranes are however expensive and prone to rapid deterioration of their thermal and physical properties, e.g. ion conductivity, when exposed to low humidity and high temperatures. Moreover, the application of a single membrane that is 25 μm or less in thickness is technically demanding due to its relative mechanical instability. To improve the performance of fuel cells, it is however necessary to reduce electrical resistance by minimizing the thickness of the polymer electrolyte membrane. In meeting this challenge, efforts have been devoted toward developing thin membranes with improved thermal and chemical stability. Hydrocarbon membranes (e.g., PEEK, polyarylene ether, PBI, etc.) and perfluorinated reinforced membranes (e.g., Gore-select, Flemion SH) have attracted attention as potential substitute for perfluorinated single membranes. These hydrocarbon membranes have lower manufacturing costs and can better withstand high temperatures and low humidity. However, their performance cannot match that of perfluorinated single membrane under humidity conditions of 100% or less and, further, their chemical stability is lower than that of perfluorinated single membranes.
The perfluorinated reinforced membranes have been contrived to solve the drawbacks of the existing perfluorinated single membranes. Such membranes manufactured by mixing perfluorinated polymer electrolytes with supports have excellent chemical stability and mechanical stability as compared with the single membranes. Moreover, it is possible to manufacture thin film membranes to reduce the membrane resistance and increase the hydrogen ion conductivity, thus enhancing overall fuel cell power. Furthermore, it is possible to increase the power density per unit area of fuel cells to reduce the amount in use of polymer electrolyte membranes in manufacturing stacks having the same power density, thus decreasing the manufacturing cost. Other potential candidates for PEMFC incorporation include reinforced membranes that use a PVDF film. However, such membranes typically have a high gas-crossover, which is presumably caused by certain weak spots in the membrane generated when the polymer electrolyte resin is not impregnated densely into the porous support during the manufacturing process, thereby negatively affecting the long-term stability of fuel cells. In light of the above, there is a need in the art for improved electrolyte membranes having better mechanical stability and ion conductivity even under low humidity and high temperatures.